Non hermetic sealed linear trimming potentiometer

ABSTRACT

A wire-wound, low-cost linear trimming potentiometer for use where a hermetically sealed unit is not required. The resistance element is a wire-wound rod with terminals stuck perpendicularly through it with each of the ends of the resistance wire welded to them. The terminals extend through openings in an open-topped shell that has slots at each end to receive a lead screw, one end of which is held by a plastic retainer. A U-shaped slider is pressed onto the lead screw and a wire clip encircles the slider and bears against the upper surface of the resistance wire. A collector bracket extends across the screw at the open side of the shell and along the entire length of the screw. The spring clip bears against the under surface of the collector, which has a terminal that extends through the shell and serves as the terminal to the arm of the potentiometer. In place of the screw, a slide actuator may be used. It is connected to the slider by pins that extend through slots in the collector.

United States Patent 1191 Berkelhamer et al.

[ 1 NON HERMETIC SEALED LINEAR TRIMMING POTENTIOMETER [75] Inventors: Louis B. Berkelhamer, Glencoe;

William H. Schapira, Skokie, both of I11.

[73] Assignee: North American Philips Corporation, New York, NY.

[22] Filed: Dec. 26, 1973 [21] Appl. No.: 427,623

Related 1.1.8. Application Data [63] Continuation of Ser. No. 110,859, Jan, 29, 1971,

abandoned.

[51] Int. Cl HOlc 5/02 [58] Field of Search 338/180, 118, 143, 148,

[56] References Cited UNITED STATES PATENTS 2,938,186 5/1960 Kassay et a1. 338/180 2,997,679 8/1961 Barden 338/180 3,050,704 8/1962 Dickinson et al.. 338/180 3,090,025 5/1963 Dole 1 338/183 3,120,650 2/1964 Blanco..... 338/202 3,134,955 5/1964 Hardison. 338/180 3,409,855 11/1968 Bender 338/118 3,412,361 11/1968 Lovejoy 3,413,590 11/1968 Woods 3,510,821 5/1970 Eberwein 338/183 14 1 Aug. 19, 1975 Primary ExaminerBruce A. Reynolds Attorney, Agem, 0r Firm-Frank R. Trifari; Leon Nigohosian [5 7] ABSTRACT A wire-wound, low-cost linear tn'mming potentiometer for use where a hermetically sealed unit is not required. The resistance element is a wire-wound rod with terminals stuck perpendicularly through it with each of the ends of the resistance wire welded to them. The terminals extend through openings in an open-topped shell that has slots at each end to receive a lead screw, one end of which is held by a plastic retainer. A U-shaped slider is pressed onto the lead screw and a wire clip encircles the slider and bears against the upper surface of the resistance wire. A collector bracket extends across the screw at the open side of the shell and along the entire length of the screw. The spring clip bears against the under surface of the collector, which has a terminal that extends through the shell and serves as the terminal to the arm of the potentiometer. In place of the screw, a slide actuator may be used. It is connected to the slider by pins that extend through slots in the collector.

12 Claims, 10 Drawing Figures 47 1111 llll 11111 2 ll 26 M NON I-IERMETIC SEALED LINEAR TRIMMING POTENTIOMETER This is a continuation of application Ser. No. 110,859, filed Jan. 29, I971, abandoned.

FIELD OF THE INVENTION This invention relates to linear trimming potentiometers and particularly to a type of low-cost potentiometer not enclosed in a hermetically sealed case.

BACKGROUND OF THE INVENTION I-Ieretofore, trimming potentiometers have generally been made in cases, or housings, that were substantially hermetically sealed to protect the resistive element and the movable contact from being contaminated by the atmosphere of the environment in which such potentiometers may be used. Sealed potentiometers are expensive because of the care that must be taken in assembling them and because of the complexity of the parts that are necessary to achieve as good a hermetic seal as possible.

However, there are many occasions when the environment is not so objectionable and it is not necessary to provide an expensive hermetic enclosure for the potentiometer. Instead, an enclosure can be used that provides only the necessary mechanical support to hold the parts in alignment for satisfactory operation. Such a potentiometer must be reasonably rugged, and it is desirable to use of wire-wound resistance element. The cost saving that results from making the potentiometer in a relatively open structure can be carried still further by providing parts that are substantial, and therefore strong, but relatively easy to assemble.

BRIEF DESCRIPTION OF THE INVENTION The trimming potentiometer of the present invention is constructed in an open-topped, rather deep shell. The resistance element consists of an insulator rod having a number of turns of resistance wire wound on it and provided with two terminals in the form of pins or relatively rigid wires held in holes that pass through the rod near each end. The ends of the resistance wire are welded to these terminal pins, and the assembly of rod, wire, and pins is inserted into the shell so that the pins extend through properly placed holes in the bottom of the shell. The inner surfaces of the shell are provided with projections that guide the rod into a specific location within the shell, and the rod may be provided with grooves or flattened surfaces to engage these projections to prevent the rod from turning. Furthermore, the rod may have a low-gabled surface along the side that faces upwardly in the shell.

Movable connection is made along the length of the wire and on the peak of the shallow gabled portion by a contact clip held in a slider that is free to move parallel to the length of the rod within the shell. The lower surface of the clip engages the wire, and an upper part of the clip that goes over the slider engages the under surface of a sheet metal collector that has a bent down side portion and a terminal that extends through a suitably placed hole in the bottom of the shell. The collector is held in place by internal projections within the shell.

The slider may be moved by a handle that has pins that extend through slots in the upper surface of the collector or by a lead screw that fits within a plastic holder that snaps into a groove in one end of the shell.

The other end of the screw is journalled in another groove at the other end of the shell and the screw fits within and makes threaded engagement with a longitudinal slot in the slider.

BRIEF DESCRIPTION OF THE DRAWINGS F10. 1 is a cross-sectional side view of one embodiment of a potentiometer constructed according to the invention;

FIG. 2 is a cross-sectional end view of the potentiometer of FIG. 1;

FIG. 3 is a top view of the potentiometer of FIGS. I and 2;

FIG. 4 is a cross-sectional view of the shell used in the potentiometer of FIGS. 1 3;

FIG. 5 is a top view of the shell in FIG. 4;

FIG. 6 is a cross-sectional side view of a modified form of potentiometer according to the invention;

FIG. 7 is a cross-sectional end view of the potentiometer of FIG. 6;

FIG. 8 is a top view of a potentiometer in FIGS. 6 and 7:

FIG. 9 is a perspective view of a collector for use in the potentiometer of FIGS. 6 8; and

FIG. 10 is a perspective view of a slide actuator for use in the potentiometer of FIGS. l3.

DETAILED DESCRIPTION OF THE DRAWINGS The potentiometer in FIG. 1 comprises an insulating rod 11 which may be of slightly deformable plastic phenolic material having a central portion 12 which is substantially round except for the upper surface. The upper surface is almost flat but has a slight ridge down the center so that it has, in effect, a low-gabled shape. The ends 13 and 14 are also round on the bottom and flattened off on the top surface in the regions 16 and 17 and along side portions 18 and 19. The ends have short spacer stubs 21 and 22 to locate the rod 11 properly within a shell 23. The flattened surfaces 16 and 17 provide space for the heads 24 and 26 of two terminals 27 and 28 which are in the form of rods or wires. These terminals are inserted through holes bored or formed in the end portions 13 and 14, and a resistance element comprising a relatively large number of turns of fine wire 29 is wound on the central portion 12 and welded to the heads 24 and 26. The rod 11 with the terminals 27 and 28 and the wire 29 forms a sub-unit of the potentiometer assembly.

The shell 23 has a slot 31 in one end 32 and another slot 33 located in the other end 34 and aligned with the slot 31. A lead screw 36 extends the full length of the shell 23 and slightly beyond. Most of the lead screw is threaded, except at one end, which has a smooth surface 37 that acts as a bearing surface in the slot 33. The other end of the screw 36 is enclosed within an annular knurled knob 38 that is pressed onto the screw and has a recess 39 into which the head 41 of the screw fits. The knob 38 also has a short shank 42 that fits into the slot 31 and is journalled therein. The end 43 of the shank extends laterally outwardly as a flange to prevent the knob from being withdrawn from the slot 31. The knob fits so tightly on the screw that rotating the knob causes the screw to turn.

A slide 44 threadedly engages the screw 36 to be moved thereby. The slide, as shown in FIG. 2, is a U- shaped structure having upwardly extending side portions 46 and 47, the latter of which has a slot 48 in one end. A wire contact spring 49 fits within the slot 48 and has a lower portion 51 that engages the resistance wire 29 along the part of each turn that passes across the central ridge in the upper part of the portion 12. The upper part 52 of the contact spring 49 presses against the under surface of a collector plate 53, which has a depending side part 54 and a terminal 56 that extends parallel to the terminal 28 through the bottom of the shell 23. The purpose of the contact spring 49 is to form a low-resistance, movable connection between the collector plate 53 and the turns of the resistance wire 29, and, for this purpose, the contact spring 49 has a generally hexagonal shape but is not a closed loop. The ends are free and the normal shape of the contact spring is such that it has to be compressed slightly when placed between the resistance wire 29 and the collector plate 53. This causes it to press firmly against both the resistance wire and the collector plate, assuring good contact with both.

The slider 44 is constrained on the top by the collector plate 53 and on one side by the depending flange 54. On the other side the slider is constrained by the inner side wall 57 of the shell 23 and by a shelf 58 in this side wall. As a result, the slider cannot twist or turn but can only move longitudinally along the shell and parallel to the axes of the screw 36 and the central portion 12 of the rod on which the resistance wire 29 is wound. The inner part of the U-shaped slider 44 between the two side portions 46 and 47 need not be formed with threads, provided the slider is made of nylon or similar insulating plastic that will sufficiently conform to the threaded surface of the screw 36. This deformation of the inner surface of the slider 44 assures that the slider will move in response to rotation of the screw just as if the slider were threaded.

Since the uppermost ends of the side portions 46 and 47 must bear on the under surface of the collector plate 53 for proper guidance of the slider 44 and yet there must be room for the upper part 52 of the contact spring 49 to bear against the collector plate 53, parts of the extremities of the side portions 46 and 47 are cut away to leave only two ends 59 and 61 as shown particularly in FIG. 1. The surfaces of these ends 59 and 61 have sufficient area to provide proper guidance of the slider 44, and by cutting away the remainder to form these ends, there is room for the upper part 52 of the contact spring to pass from one side to the other and thus substantially encircle the screw 36.

As shown in FIGS. 3 and 9, the collector plate 53 has a slot 62. This slot is almost as long as the collector plate itself and is substantially centered over the upwardly extending portion 47 but is not as wide as that portion. Therefore, the edges of the upwardly extending portion 47 can press on those parts of the collector plate 53 on each side of the slot 62. One of the main purposes of the slot is to provide easy access for degreasing chemicals to reach the interior of the shell 23.

FIGS. 4 and show some of the internal construction of the shell 23. In particular, four projections 63 66 are located on the inner walls of the shell 23 and help hold the collector plate 53 in place. The depending portion of the collector plate fits between the inner wall 67 and a pair of upright bars 68 and 69 that extend from the end walls 32 and 34, respectively. The free end of the collector plate 53 rests on another pair of upright corner members 73 and 74 so that the entire collector and the flange 54 attached to it are securely held.

On the inner surface of the end walls 32 and 34 are two elongated bar projections 76 and 77 that help to hold the ends 13 and 14 of the rod 11 in place. At the bottom of the shell are two openings 81 and 82 through which the terminals 27 and 28, respectively, extend and between these two openings and off to one side is another, rectangular opening 83 thl ugh which the terminal 56 of the collector extends. The slot 33 in the end wall 34 has an upper portion that is narrower than the lower part that acts as the support for the reduced diameter end 37 of the screw 36. This permits the screw to be forced into place and to rotate easily once it is in place but prevents it from being removed accidentally. The other slot 31 in the other end wall 32 has the same configuration as the slot 33 except that it is somewhat wider to accommodate the shank 42 of the knob 38.

FIGS. 6 through 8 show a potentiometer without a lead screw but which is otherwise similar to the potentiometer of FIGS. 1 3. The parts of the potentiometer in FIGS. 6 8 that are similar to those in FIG. 1 3 will not be described in detail but are indicated by the same reference numerals as in the previous figures.

The slider 44, which is shown particularly in FIGS. 6 and 7, is moved along the length of the rod 11 by a slide actuator 86. The slide actuator is shown in FIGS. 6 8 as part of the complete potentiometer, but it is perhaps better shown in FIG. 10. It includes a handle 87 to be grasped to move it along the length of the potentiometer and two pins 88 and 89 that extend from the underside of the actuator and into matching holes in the upper ends 59 and 61 of the slider 44. The collector plate in the potentiometer of FIGS. 6 a 8 is indicated by reference numeral 153 since it differs from the collector plate 53 of the embodiment of FIGS. 1 3 by virtue of having two longitudinal slots 62 and 91. The latter slot is provided so that the pin 88 can connect the slide actuator 86 to the upper end 59. The other pin 89 extends through the slot 62 and into the upper end 61.

The setting of the contact spring 49 in the embodiment of the potentiometer in FIGS. 6 8 is more direct than the setting of the contact spring 49 in the embodiment of FIGS. 1 3. However this fact also means that it may be more difficult to set the contact spring to a precise resistance value in the embodiment in FIGS. 6 8 than in the embodiment in FIGS. 1 3. In those cases in which accuracy is more important than speed, the embodiment of FIGS. 1 3 is more likely to be used; but in cases in which the speed of setting is more important or in which it is desired to have some mechanical means grasp the handle 87 and adjust the setting, the embodiment of FIGS. 6 8 will usually be preferred. It is also possible, by making the pins 88 and 89 in the embodiment of FIGS. 6 8 somewhat less of a force fit in the holes in the slider 44 to pull the actuator 86 out after it has been moved to a specific setting and thereby prevent any variation in the setting of the potentiometer.

What is claimed is:

1. A potentiometer comprising:

A. An elongated resistive element including an elongated insulating member and a plurality of turns of resistance wire wound thereon, said insulating member having a central cylindrical portion which in turn has a substantially flat portion of the upper surface, said substantially flat portion including a central longitudinal ridge, said turns of resistance wire being tautly wound across said ridge.

B. A shell in which said resistive element is fixedly located, said shell comprising:

1. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of the side walls and the bottom wall to form an opentopped shell surrounding said resistive element;

C. A conductive collector plate extending parallel to said resistive element across the top of said shell and mechanically connected to said walls to cooperate with said wall and said resistive element to form a substantially enclosed space;

D. A slider positioned directly between said resistive element and said collector plate and logitudinally movable within said enclosed space along the length of said resistive element;

E. A contact spring attached to said slide to move therewith and comprising one portion resiliently contacting the ridge position of said resistive element and another portion resiliently engaging the proximal surface of said collector plate and F. Means to move the slider along its range of travel.

2. The potentiometer of claim 1 comprising, in addition:

A. Holes through said end portions;

B. Matching holes through said bottom wall aligned with said holes through said end portions; and

C. Terminal rods extending through said holes in said end portions and in said bottom wall, the ends of said resistance wire being connected to said terminal rods.

3. The potentiometer of claim 1 comprising, in addi tion, a longitudinal shelf extending along one of said side walls, one edge of said slider resting thereon, the spacing between said shelf and said collector plate being just sufficient to allow said slider to move freely along said shelf.

4. The potentiometer of claim 1 in which said means to move said slider comprises:

A. A lead screw journalled in said end walls and extending, parallel to said resistive elements between said resistive element and said collector plate; and

B. A bushing fitting closely around said screw and engaging one of said end walls, said bushing comprising a deformable plastic having an enlarged outer flange and an inner flange and a neck between said flanges, said one end wall having a slot into which said neck fits.

5. The potentiometer of claim 1 in which said collector plate is generally L-shaped and comprises:

A. A flange that extends down inside said shell alongside one of said walls; and

B. A terminal extends downward from said flange,

and said bottom has a hole through which said terminal extends.

6. The potentiometer of claim 5 in which said collector plate comprises a top flat portion that extends across the open end of said shell and comprises a longitudinal slot that extends parallel to said resistive element.

7. A potentiometer comprising A. An elongated resistive element B. A shell in which said resistive element is fixedly located, said shell comprising:

l. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of said side walls and said bottom wall to form an opentopped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element; E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate; and F. Means to move said slider along its range of travel comprising 1. a lead screw journalled in said end walls and extending parallel to said resistive element and said end collector plate; and

2. a bushing fitting closely around said screw and engaging one of said end walls, said bushing including a deformable plastic having an outer flange, an inner flange and a neck between said flanges, said one end wall into which the neck fits having a slot into which said neck fits, said slotcontaining end wall also having an enlarged closed end fitting more than halfway around said neck.

8. The potentiometer of claim 7 in which said screw has a head engaging said outer flange on said bushing and a smooth cylindrical surface on the other end.

9. A potentiometer comprising:

A. An elongated resistive element;

B. A shell in which said resistive element is fixedly located, said shell comprising:

1. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of said side walls and said bottom wall to form an pentopped shell surrounding said resistive el lent;

C. A conductive collector plate extending par el to said resistive element across the open top if said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space, said collector plate generally L-shaped and comprising a flange that extends down inside said shell alongside one of said side walls, said flange having a terminal extending downward therefrom, said bottom wall having an opening through which the terminal extends, said collector plate also including a top flat portion which extends across the open end of said shell and having a longitudinal slot extending parallel to the resistance element;

D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element;

E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate;

F. Means to move said slider along its range of travel; and wherein said shell also comprises a pair of vertical columns integral with each of said end walls and said one of said side walls to guide and hold said flange of said collector alongside said resistive element but space and electrically insulated therefrom.

10. A potentiometer comprising:

A. An elongated resistive element;

B. A shell in which said resistive element is fixedly located, said shell comprising:

l. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of the side walls and the bottom wall to form an opentopped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element, and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element said slider comprising a U-shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of said side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members: E. A contact spring attached to said slider to move therewith and comprising one portion reliliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate, said contact spring having a straight central portion and having bent over ends and wherein said shorter portion of one of said side members of said slider having a vertical channel extending therethrough to receive the central part of said contact spring and wherein said slider includes second and third vertical channels in the diagonally opposite portion of said slider from said first named vertical channel, the endmost portion of said bent over ends of said contact spring extending into said second and third channels respectively; and F. Means to move said slider along its range of travel. 1]. A potentiometer comprising: A. An elongated resistive element; B. A shell in which said resistive element is fixedly located, said shell comprising 1. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of the side walls and the bottom wall to form an opentopped shell surrounding said resistive element;

C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space;

D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element, said slider comprising a U- shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of said side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members:

E. A contact spring attanched to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate;

F. Means to move said slider along its range of travel;

and

G. A slider actuator comprising means extending through said collector plate to engage the uppermost corner portions of said slider to move said slider longitudinally along said resistive element.

12. A potentiometer comprising:

A. An elongated resistive element;

B. A shell in which said resistive element is fixedly located, said shell comprising:

1. a pair of side walls and a bottom wall substantially parallel to said resistive element, and

2. a pair of end walls joining the ends of the side walls and the bottom wall to form an opentopped shell surrounding said resistive element;

C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space;

D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element, said slider comprising a U- shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members;

E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate;

F. Means to move said slider along its range of travel;

and

G. A slider actuator comprising means extending through said collector plate to engage the uppermost corner portions of said slider to move said slider longitudinally along said resistive element; and

in which said collector plate comprises first and second parallel longitudinal slots, and said comer portions of said slider have first and second recesses in them laterally spaced the same distance as said slots in said collector plate, and said slide actuator comprises a handle portion and first and second projections extending through said slots and engaging said first and second recesses, respectively.

1 l IO! IF 

1. A potentiometer comprising: A. An elongated resistive element including an elongated insulating member and a plurality of turns of resistance wire wound thereon, said insulating member having a central cylindrical portion which in turn has a substantially flat portion of the upper surface, said substantially flat portion including a central longitudinal ridge, said turns of resistance wire being tautly wound across said ridge. B. A shell in which said resistive element is fixedly located, said shell comprising:
 1. a pair of side walls and a bottom wall substantially parallel to said resistive element, and
 2. a pair of end walls joining the ends of the side walls and the bottom wall to form an open-topped shell surrounding said resistIve element; C. A conductive collector plate extending parallel to said resistive element across the top of said shell and mechanically connected to said walls to cooperate with said wall and said resistive element to form a substantially enclosed space; D. A slider positioned directly between said resistive element and said collector plate and logitudinally movable within said enclosed space along the length of said resistive element; E. A contact spring attached to said slide to move therewith and comprising one portion resiliently contacting the ridge position of said resistive element and another portion resiliently engaging the proximal surface of said collector plate and F. Means to move the slider along its range of travel.
 2. a pair of end walls joining the ends of the side walls and the bottom wall to form an open-topped shell surrounding said resistIve element; C. A conductive collector plate extending parallel to said resistive element across the top of said shell and mechanically connected to said walls to cooperate with said wall and said resistive element to form a substantially enclosed space; D. A slider positioned directly between said resistive element and said collector plate and logitudinally movable within said enclosed space along the length of said resistive element; E. A contact spring attached to said slide to move therewith and comprising one portion resiliently contacting the ridge position of said resistive element and another portion resiliently engaging the proximal surface of said collector plate and F. Means to move the slider along its range of travel.
 2. The potentiometer of claim 1 comprising, in addition: A. Holes through said end portions; B. Matching holes through said bottom wall aligned with said holes through said end portions; and C. Terminal rods extending through said holes in said end portions and in said bottom wall, the ends of said resistance wire being connected to said terminal rods.
 2. a pair of end walls joining the ends of the side walls and the bottom wall to form an open-topped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element, said slider comprising a U-shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members; E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate; F. Means to move said slider along its range of travel; and G. A slider actuator comprising means extending through said collector plate to engage the uppermost corner portions of said slider to move said slider longitudinally along said resistive element; and in which said collector plate comprises first and second parallel longitudinal slotS, and said corner portions of said slider have first and second recesses in them laterally spaced the same distance as said slots in said collector plate, and said slide actuator comprises a handle portion and first and second projections extending through said slots and engaging said first and second recesses, respectively.
 2. a pair of end walls joining the ends of the side walls and the bottom wall to form an open-topped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element, said slider comprising a U-shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of said side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members: E. A contact spring attanched to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate; F. Means to move said slider along its range of travel; and G. A slider actuator comprising means extending through said collector plate to engage the uppermost corner portions of said slider to move said slider longitudinally along said resistive element.
 2. a pair of end walls joining the ends of the side walls and the bottom wall to form an open-topped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element, and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element said slider comprising a U-shaped member having first and second upwardly extending side members joined by a lower member, the external lateral dimension of said side members being slightly less than the distance between said side walls to allow said slider to slide freely, and diagonally opposite portions of the upper ends of the side members being shorter than the remaining portions of the side members: E. A contact spring attached to said slider to move therewith and comprising one portion reliliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate, said contact spring having a straight central portion and having bent over ends and wherein said shorter portion of one of said side members of said slider having a vertical channel extending therethrough to receive the central part of said contact sPring and wherein said slider includes second and third vertical channels in the diagonally opposite portion of said slider from said first named vertical channel, the endmost portion of said bent over ends of said contact spring extending into said second and third channels respectively; and F. Means to move said slider along its range of travel.
 2. a pair of end walls joining the ends of said side walls and said bottom wall to form an open-topped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space, said collector plate generally L-shaped and comprising a flange that extends down inside said shell along-side one of said side walls, said flange having a terminal extending downward therefrom, said bottom wall having an opening through which the terminal extends, said collector plate also including a top flat portion which extends across the open end of said shell and having a longitudinal slot extending parallel to the resistance element; D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element; E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate; F. Means to move said slider along its range of travel; and wherein said shell also comprises a pair of vertical columns integral with each of said end walls and said one of said side walls to guide and hold said flange of said collector alongside said resistive element but space and electrically insulated therefrom.
 2. a bushing fitting closely around said screw and engaging one of said end walls, said bushing including a deformable plastic having an outer flange, an inner flange and a neck between saiD flanges, said one end wall into which the neck fits having a slot into which said neck fits, said slot-containing end wall also having an enlarged closed end fitting more than halfway around said neck.
 2. a pair of end walls joining the ends of said side walls and said bottom wall to form an open-topped shell surrounding said resistive element; C. A conductive collector plate extending parallel to said resistive element across the open top of said shell and mechanically connected to said walls to cooperate with said walls and said resistive element to form a substantially enclosed space; D. A slider directly between said resistive element and said collector plate and longitudinally movable within said enclosed space along the length of said resistive element; E. A contact spring attached to said slider to move therewith and comprising one portion resiliently engaging the proximal surface of said resistive element and another portion resiliently engaging the juxtaposed surface of said collector plate; and F. Means to move said slider along its range of travel comprising
 3. The potentiometer of claim 1 comprising, in addition, a longitudinal shelf extending along one of said side walls, one edge of said slider resting thereon, the spacing between said shelf and said collector plate being just sufficient to allow said slider to move freely along said shelf.
 4. The potentiometer of claim 1 in which said means to move said slider comprises: A. A lead screw journalled in said end walls and extending parallel to said resistive elements between said resistive element and said collector plate; and B. A bushing fitting closely around said screw and engaging one of said end walls, said bushing comprising a deformable plastic having an enlarged outer flange and an inner flange and a neck between said flanges, said one end wall having a slot into which said neck fits.
 5. The potentiometer of claim 1 in which said collector plate is generally L-shaped and comprises: A. A flange that extends down inside said shell alongside one of said walls; and B. A terminal extends downward from said flange, and said bottom has a hole through which said terminal extends.
 6. The potentiometer of claim 5 in which said collector plate comprises a top flat portion that extends across the open end of said shell and comprises a longitudinal slot that extends parallel to said resistive element.
 7. A potentiometer comprising A. An elongated resistive element B. A shell in which said resistive element is fixedly located, said shell comprising:
 8. The potentiometer of claim 7 in which said screw has a head engaging said outer flange on said bushing and a smooth cylindrical surface on the other end.
 9. A potentiometer comprising: A. An elongated resistive element; B. A shell in which said resistive element is fixedly located, said shell comprising:
 10. A potentiometer comprising: A. An elongated resistive element; B. A shell in which said resistive element is fixedly located, said shell comprising:
 11. A potentiometer comprising: A. An elongated resistive element; B. A shell in which said resistive element is fixedly located, said shell comprising
 12. A potentiometer comprising: A. An elongated resistive element; B. A shell in which said resistive element is fixedly located, said shell comprising: 